Wood floor systems used for sports, such as basketball, require a significant degree of cushioning or impact absorption of the floor relative to the underlying base of concrete or like material to which it is secured in order to reduce injuries. Accordingly, a number of different floor systems have been designed to provide appropriate floor deflection and resiliency. Such floor systems typically include a plurality of hardwood floorboards, one or more subfloor layers supporting the floorboards, and a plurality of elastomeric pads attached to and underlying the subfloor layer(s) for supporting the floor system on a base, usually in the form of a concrete or asphalt slab. In some cases, the base may be a pre-existing wood floor. The floor system is anchored to the base by metal fasteners in such a way as not to precompress the elastomeric pads when the floor system is in an unloaded state and leaving a gap of free space between the subfloor(s) and the base with the vertical dimension of that space being such as to allow downward deflection of the floor under impact, thereby providing shock absorption and resiliency or “give”, and reducing the amount of reaction force imparted by the floor system to the impacting person or object.
The free space provided between the subfloor layers and the base is also important with respect to reducing the effect of humidity changes on the dimensional stability of the wood components. Wood components are susceptible to absorption and expulsion of moisture, with a resultant expansion and contraction. The effect of humidity changes on the dimensional stability of the floor system is reduced by the free space inasmuch as the latter limits moisture transfer between the base and the supported components.
A number of different floor systems are known that are designed to provide some degree of impact absorption and are characterized by free space between the base and the subfloor layers. One of those systems is disclosed in U.S. Pat. No. RE37,615, issued Apr. 2, 2002 to Michael W. Niese for “Anchored/Resilient Hardwood Floor System”. The disclosure of that patent is incorporated herein by reference.
In the construction disclosed and claimed in U.S. Pat. No. RE37,615, a plurality of mutually spaced sleepers 20 (FIGS. 1 and 2) in the form of elongated nailing members are used with a subfloor layer 22 for supporting a layer of hardwood floorboards 24 that serve as a wear surface. One or more of the subfloor layers 22 are interposed between the sleepers 20 and the hardwood wear surface 24. The sleepers 20 also include compressible supporting pads 26, e.g., pads made of a suitable elastomer. In the floor system disclosed in the aforesaid patent, a fastening arrangement 30 is used to secure the sleepers 20 directly to a base 28 so that (a) the pads 26 are not precompressed, i.e., the pads are not compressed beyond the compression that results solely from the weight of the flooring system components carried by the pads, and (b) the sleepers 20 can deflect downwardly upon impact to the upper layer of the floor system but are restricted against upward movement beyond the initial static position of the pads. The fastening arrangement 30 includes holes 32 with counterbores 44 in the sleepers 20, floor-anchoring fasteners 34 with heads 40 that extend through the counterbored holes 32 into the base 28, and means 36 for limiting the depth of penetration of the fasteners 34 into the base 28 so that the downward driving forces applied via the fasteners do not precompress the elastomer pads 26. As disclosed in U.S. Pat. No. RE37615, cited supra, the means 36 comprises a cylindrical plastic lubricating sleeve 36 which may but need not have an integral flange 42 (as shown in FIG. 9 of the patent) or be used with a separately formed flange in the form of a circular washer (FIG. 1). Counterbore 44 is sized to accommodate fastener head 40 and also flange 42. U.S. Pat .No. RE37615 teaches that the sleeve 36 may be made of Teflon or any other low friction material.
Floor systems similar to the type shown and described in U.S. Pat. No. RE37,615 are in commercial use. The foregoing patent indicates that the floor system disclosed therein may be anchored by forcing the fasteners 34 into predrilled holes 38 in the base 28 or by driving the fasteners into the base using a nail gun without any pre-drilled holes. However, as a practical matter prior to this invention it was not feasible or practical to anchor the sleepers to a concrete base without first predrilling holes for the fasteners in the concrete. Instead, the usual practice has been to predrill holes in the concrete base and use fasteners that are characterized by a shoulder that functions as a depth stop and an expansion curve adjacent the leading end for anchoring the fasteners in the concrete base, with the fasteners being surrounded by plastic lubricating sleeves that sit loosely in the counterbored holes and serve to reduce friction between the fasteners and the sleepers, as illustrated in FIG. 9 of U.S. Pat. No. RE37,615. Typically, the lubricating sleeve has a peripheral flange at its top end and the flange portion has a counterbore to accommodate the head of the fastener. The fasteners are driven into the predrilled holes by manually impacting them with a hammer.
Manually driving a fastener into dense concrete without predrilling a hole to accommodate the fastener cannot be done, or at least not without having to strike each fastener repeatedly. However, the holding power of a fastener driven into solid concrete by repeated blows is unsatisfactory. When a fastener is impacted with sufficient force to penetrate a concrete substrate, a so-called “ball” is formed in the concrete around the leading end of the fastener. That ball is a densification of the concrete which exerts a tight grip on the fastener. However, if thereafter the embedded fastener is impacted one or more times, the ball will be disrupted and even disintegrate, with the result that the concrete's grip on the fastener is weakened substantially. It is well known in the structural fastening field that the same phenomenon occurs when impact driving a fastener into a steel substrate. Therefore, to maximize the holding power, a fastener should not be hit more than once when impact driven into concrete or steel.
Heretofore powered impact-type drivers have been used for driving fasteners into concrete or other hard masonry substrates for the purpose of anchoring metal components to the substrates. However, prior to this invention use of power drivers for anchoring the sleepers disclosed in U.S. Pat. No. RE37,615 was not feasible. The primary problem stems from the counterbored holes 32 in the sleepers 20. The counterbored holes 32 are designed to accommodate heads 40 of the fasteners 34 so they will not protrude above the sleepers where they can interfere with the subfloor members 22 carried by the sleepers, particularly when the floor system is deflected downwardly under impact. The counterbores 44 serve to provide a recessed seat for the flanges 42.
However, the requirement that the heads 40 of the fasteners (and also the flanges 42 of the lubricating sleeves 36 when used) be recessed in the counterbored holes 32 has made it difficult to use a power driver. The need to recess the heads of the fasteners in the counterbored holes 32 complicates attainment of the requirement that the striker or hammer of the power driver be able to drive the fasteners deep enough to assure a tight engagement of the fastener heads (or the flanges of the lubricating sleeves) with the bottoms of the counterbores, but not so deep as to preload the resilient pads 26. The counterbored holes 32 also make it difficult to center the striker or hammer of the powered driver on the fastener head, which is an important consideration since optimum performance of the driver requires that its striker be readily centered on the fastener head and the driver be positioned to drive the fastener perpendicularly to the base 28. This centering problem is complicated by the fact that in actual practice the lubricating sleeves 36 are sized to make a loose fit in the counterbored holes. Another factor discouraging against use of a power driver is the requirement that the action of the driver not interfere with the use of fastener depth stop means designed to prevent compression of the resilient pads, as those disclosed in U.S. Pat. No. RE37,615.
Because of these problems, there has been lacking a satisfactory and reliable way to secure the sleepers of the form disclosed in the aforesaid patent to a concrete base without using pre-drilled holes for the fasteners. The need to predrill holes introduces a variety of limitations, the most significant of which is that installation of such systems is slow and costly due to the manual labor consumed in predrilling holes in the concrete and the need to precisely locate the holes to assure alignment with the counterbored holes in the sleepers, and the repeated hammering action required to seat the fastener.
One solution that has been advanced is described in my copending application Ser. No. 10/301,262, cited supra. The invention described in that application constitutes a substantial improvement over the prior art in that it facilitates use of a power driver. The present invention constitutes an improvement over the invention disclosed in my copending application Ser. No. 10/301,262.